Soil-plant nutrient balance of tea crops in the northern mountainous region, Vietnam

Unbalance of nutrients in soil-plant system is considered a cause of soil quality degradation in long-term tea cultivation in the northern mountainous region, Vietnam. The objective of this study was to measure the nutrient balance between plant removals, recycling, storage and addition in different tea age classes (10, 25 and 40 years old). Plant biomass and plant nutrient concentrations were measured for calculation of plant nutrient uptake. Nutrients accumulated in the plants and removed from harvest were considered as nutrient loss, while fertilizer was considered as nutrient inputs gain to soil. Plant nutrient concentrations such as N, P, K, S and Mg in the tea stands decreased in the order: young leaves (and buds) > mature leaves > branches > stems. Age of the tea plantations had no significant effect on tissue concentrations of N, Ca, or Mg. However, there were significant differences between tea age classes for K (in both the young and mature leaves) and for P and S (in the mature leaves). The results from the study also showed that fertilizer inputs meet the crop nutrient demands (nutrient loss from harvest). However, if some other nutrient pools (e.g. nutrient leaching, storage in the plants) are accounted for the total nutrient budget, these inputs of fertilizer may not be enough to balance total nutrient losses.